Chemiluminescence during decomposition of dimethyldioxirane

Chemiluminescence in the visible spectral region during decomposition of dimethyldioxirane in a cumene-acetone mixture at 22–52 °C has been detected. Arrhenius parameters of this process have been obtained.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, p. 1395, July, 1995.     

Kinetics of thermal decomposition of dimethyldioxirane in oxygen atmosphere

Dimethyldioxirane decomposition in oxygen atmosphere follows a first-order kinetic law. Decomposition rate constant (k, s⁻¹) in acetone in the temperature range from 30 to 50°C has been determined as lgk=(7.1±0.9)−(16.0±1.4)/θ, θ=2.303RT kcal/mol.     

Kinetics and mechanism of the reaction of dimethyldioxirane with cumene

The reaction of dimethyldioxirane with cumene (22–52°C) follows a chain-radical mechanism. The kinetic regularities of this reaction were studied by the chemiluminescence and kinetic UV spectrophotometry methods by monitoring the consumption of dioxirane. The process is inhibited by oxygen. In the absence of O₂, the process is accelerated due to the decomposition of dimethyldioxirane induced by alkyl radicals. In this case, the reaction occurs according to a complicated kinetic law including the first and second orders with respect to dioxirane. Based on the kinetics and reaction products, the scheme of the process was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 694–702, April, 1997.     

Products, kinetic regularities, and mechanism of thermal decomposition of ethyl(methyl)dioxirane

The products and kinetic regularities of thermal decomposition of ethyl(methyl)dioxirane (EMD) were studied. The consumption of EMD occurs via four parallel pathways: two isomerizations to ethyl acetate and methyl propionate, solvent oxidation via insertion of the oxygen atom into the C-H bond of a solvent molecule (butanone), and hydrogen atom abstraction from the solvent by dioxirane with radical escape from the cage. The contribution of the latter route to the oxidation of butan-2-one at 35 °C is 43%. Alkyl radicals initiate EMD decomposition in an inert atmosphere. The activation parameters of EMD isomerization to esters and the reaction of EMD with butanone were determined. The isomerization of EMD was studied by the DFT method. The geometric parameters were optimized at the UB3LYP level using the 6-31G** and/or 6-311+G** basis sets. The calculated energies were corrected taking into account zero-point vibrations. The theoretical results are in good agreement with experimental data. The mechanism of EMD thermolysis is considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1716–1723, October, 2006.     

The thermal decomposition of the carbonate reaction products

The complex thermal analysis was used in the investigations of the carbonate reaction products in the residue after Al leaching from calcium aluminate-12CaO·7Al₂O₃ and Selfdisintegrated Powder. The conversion of Al was calculated basing on a content of Al in the pregnant solution as well as in a residue obtained from the kinetic investigations. The third method of measurements of a conversion of Al was presented and discussed. Results show, that the proposed method can be used for conversion estimations with 95% of confidence level as well as for the detection of carbonate products and is useful for an interpretation of the new approach for kinetic mechanism of Al leaching.     

Kinetics of the reaction between dimethyldioxirane and 2-methylbutane

The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O₂, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10⁻⁴ s⁻¹) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between the alkyl radical and dimethyldioxirane was estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1785–1788, October, 1997.     

Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate

The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO₃ formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N₂O₃ and NH₃OH⁺, whereas the subsequent acceleration is due to oxidation of NH₃OH⁺ by nitrogen oxides formed as well as by nitrous acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1897–1901, November, 1993.     

The thermal decomposition of N,N-dimethyl-3-oxa-glutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by 1H-NMR, Fourier transform in-frared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The ki-netic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1-α) 1/3-1]-1, 203.75 kJ-mol-1 and 1017.95s-1, respec-tively. The values of ΔS≠, ΔH≠ andΔG≠ of the reaction are 94.28 J-mol-1-K-1, 203.75 kJ-mol-1 and 155.75 kJ-mol-1, respectively.     

Kinetics and mechanism of the thermal decomposition of barium titanyl oxalate

Thermal analysis of barium titanyl oxalate reveals that the decomposition proceeds through four distinct rate processes. Among them, the decomposition of oxalate occurs in the temperature range 230–350°C, and has been studied by TG and gas pressure measurements, supplemented by IR spectroscopy, electron microscopy and chemical analysis. Oxalate decomposition proceeds differently in vacuum and in flowing gas atmospheres. Analytical results indicate the formation of a complex carbonate together with CO, CO₂ and water vapour below 400°C. Schemes for each type of decomposition are proposed and discussed. For decomposition in vacuum, kinetic observations fitted the three-dimensional, diffusion controlled, rate equation for almost the entire α-range (0.028≤α≤0.92). The activation energy is calculated to be3 189±6 kJ mol⁻¹. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Synthesis and kinetic regularities of the thermal decomposition of new hydrotrioxides of cyclic alcohols

Cyclic hydrotrioxides were synthesized by low-temperature (?78 °C) ozonolysis of a series of cyclic alcohols and identified using ¹H NMR spectra. The kinetic regularities of the thermal decomposition of the synthesized hydrotrioxides were studied. The experimental proof of the induced decomposition of alcohol hydrotrioxides was obtained for the first time using cyclohexanol hydrotrioxide as an example. The influence of cyclic substituents on the thermal stability of the hydrotrioxides is shown.     

Elucidating the mechanism of the asymmetric aza-Michael reaction

The mechanism of the palladium-catalysed asymmetric aza-Michael addition of aniline to alpha,beta-unsaturated N-imide was examined from several aspects using a combination of techniques, including X-ray crystallography, mass spectrometry, NMR, UV/Vis spectroscopy, and kinetic studies. The binding of aniline to the dicationic palladium(II) metal centre was found to occur in two consecutive steps: The binding of the first aniline is fast and reversible, whereas the binding of the second aniline is slower and irreversible. This occurs in competition with the binding of the N-imide, which forms a planar six-membered chelate ring with the metal centre; coordinating through the 1,3-dicarbonyl moiety. Isotopic labelling revealed that the addition of N-H occurs in a highly stereoselective manner, allowing the synthesis of optically active beta(2)- and beta(2,3)-amino acid derivatives. The stereochemistry of the addition is postulated to be syn. In situ kinetic studies provided evidence for product inhibition. The binding of the N-imide to the catalyst was found to be the rate-limiting step. Aniline was found to be an inhibitor of the pre-catalyst. The study culminated in the design of a new reaction protocol. By maintaining a low concentration of the aniline substrate during the course of the reaction, significant enhancement of yield and enantioselectivity can be achieved.     

Synthesis of hydrated furans: Analysis of the Prins reaction mechanism

Mechanistic analysis of hydrogenated furan synthesis by the Prins reaction was carried out using mathematical modeling. The direct and inverse chemical kinetic problems are solved for the rate constants of all elementary steps. A probable mechanism is derived from the obtained quantitative kinetic parameters and the kinetic patterns of the reaction. These include kinetic curves from the concentration changes of all species in the reaction.     

Thermochemical and kinetic analysis of the thermal decomposition of monomethylhydrazine: an elementary reaction mechanism

The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemical properties were determined by ab initio and density functional calculations. The entropies, S degrees (298.15 K), and heat capacities, Cp degrees (T) (0 < or = T/K < or = 1500), from vibrational, translational, and external rotational contributions were calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S degrees (298.15 K) and Cp degrees (T) were calculated by solving the Schr?dinger equation with free rotor wave functions, and the partition coefficients were treated by direct integration over energy levels of the internal rotation potentials. Enthalpies of formation, DeltafH degrees (298.15 K), for the parent MMH (CH3NHNH2) and its corresponding radicals CH3N*NH2, CH3NHN*H, and C*H2NHNH2 were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol(-1) by use of isodesmic reaction analysis and various ab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactions of MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined by high level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermally activated MMH to dissociation products were calculated as functions of pressure and temperature. An elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed to model the experimental data on the overall MMH thermal decomposition rate. The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions.     

Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.     

Theoretical study on the reaction mechanism of CN radical with ketene

The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.     

Theoretical study on reaction mechanism of isocyanate radical NCO with ethene

The NCO + C₂H₄ reaction is simple and prototype for reaction of the NCO radical with unsaturated hydrocarbons, and it is considered to be important in fuel‐rich combustion. In this article, we for the first time perform detailed theoretical investigations for its reaction mechanism based on Gaussian‐3//B3LYP scheme covering various entrance and decomposition channels. The most favorable channel is firstly the NCO and C₂H₄ approach each other, forming a weakly‐bound complex L1 OCN···C₂H₄, followed by the formation of isomer L2 OCNCH₂CH₂ via a small barrier of 1.3 kcal/mol. Transition states of any decomposable or isomeric channels for L2 in energy are much higher than reactants, which indicate that adduct L2 has stabilization effect in this NCO + C₂H₄ reaction. The direct H‐abstraction channel leading to P1 HNCO + C₂H₃, might have an important contribution to the eventual products in high temperature. These results can well explain available kinetic experiment. Moreover, reaction mechanism for the title reaction is significantly different from the NCO + C₂H₂ reaction which proceeds on most favorably to generate the products HCN + HCCO and OCCHCN + H via a four‐membered ring intermediate. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Dominant reaction channels and the mechanism of silane decomposition in a H2-Si(s)-SiH4 glow discharge

Chemical relaxation mass spectrometry has been used to study the kinetics and mechanism in the silane-hydrogen-solid silicon system under conditions of glow discharge. The emphasis was on the main processes related to the deposition of amorphous and nanocrystalline silicon thin films. It is shown that under conditions of the deposition of a-Si and nc-Si the dominant reaction channel is the electron impact induced fragmentation of silane into molecular hydrogen and SiH₂ radical. The role of other processes, such as hydrogen abstraction, is discussed.     

Gaseous reaction mechanism of C2F radical with water

The kinetic properties of the carbon-fluorine radicals are little understood except those of CFn (n =1-3). In this article, a detailed mechanistic study was reported on the gas-phase reaction between the simplest pi-bonded C2F radical and water as the first attempt to understand the chemical reactivity of the C2F radical. Various reaction channels are considered. The most kinetically competitive channel is the quasi-direct hydrogen-abstraction route forming P5 HCCF + OH. At the CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311G(d,p)+ZPVE, CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE and Gaussian-3//B3LYP/6-31G(d) levels, the overall H-abstraction barriers (4.5, 4.7, and 4.2 kcal/mol) for the C2F + H2O reaction are comparable to the corresponding values (5.5, 3.7, and 5.7 kcal/mol) for the analogous C2H + H2O reaction. This suggests that C2F is a reactive radical like the extensively studied C2H, in contrast to the situation of the CF and CF2 radicals that have much lower reactivity than the corresponding hydrocarbon species. Thus, the C2F radical is expected to play an important role in the combustion processes of the carbon-fluorine chemistry. Furthermore, addition of a second H2O can catalyze the reaction with the H-abstraction barrier significantly reduced to a marginally zero value (0.5 kcal/mol). This is also indicative of the potential relevance of the title reactions in the low-temperature atmospheric chemistry.     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.